An analysis of magnetic susceptibility and natural gamma radioactivity is presented as indirect proxies of the characteristics of sandstones and limestones of the Sabinas basin. These rocks are located in the sedimentary sequence ranging from the Upper Jurassic to the Cretaceous. The magnetic susceptibility indicates changes in the magnetic composition of these rocks and suggests changes in their weathering degree. Ranges of values of magnetic susceptibility in sandstones and limestones allow classifying them into different groups, suggesting variability regarding conditions of origin and evolution. High values of magnetic susceptibility in limestones can be linked to sedimentation in anoxic or reducing environment, as well as with its siliciclastic content. The natural gamma radioactivity expressed in the contents of Th and relationships U / K and Th / U also suggest the degree of weathering of these rocks, mainly in the sandstones. These relations also highlight others characteristics in the sandstones related the probable provenance of sediments, its distance, degree of weathering and transport dynamics. Using the values of U / K ratio in the sandstones, it is possible to suggest the probable quartz-feldspar relationships. These ratio values classified rocks as arkose or quartzarenite, indicating the maturity of the sandstones. According to the U / K ratio values, most of these rocks which show little maturity are called arkose. Using the values of the Th / U ratio, it is possible to suggest the textures of quartzarenites, classifying them as rocks with fabric that is clast-supported or matrix-supported.
The Cerro Marcelinos (CM) and Cerro Colorado (CC) plutons are part of the Candela-Monclova intrusive belt (NE Mexico), which is mid-Eocene in age (43-35 Ma). It intrudes into the Sabinas Basin, primarily made up of limestones, of Lower and Upper Cretaceous age. Around several intrusions, including the CM and CC plutons, mineralizations are known. However, how much hidden mineralizations would occur is not known. Trends within the plutons and in contact aureoles are also poorly described at present. Therefore, we provide here in situ magnetic susceptibility (MS) and gamma ray spectrometry (GS) data along two composite transects, one in each pluton, to delineate such potential trends. The data show variations of 0.003 × 10-3 SI and 104 × 10-3 in MS and of 7.1 nGy/h and 196 nGy/h in GS with a clear relation to rock type and amount of metasomatism. The radioactive contents in the outcrops of contact metamorphic rocks indicate a contact metasomatism with differing degrees of alteration during emplacement of the plutons. The host limestones have magnetic minerals incorporated during the intrusion process. MS and GS indicate an increase in the degree of acidity towards the center of both plutons, possibly associated with the later stages of the magmatic differentiation process. The MS could divide the igneous rocks into two groups, weakly magnetic (group 1 with MS ≤ 3 × 10-3 SI) and strongly magnetic (group 2 with MS > 3 × 10-3 SI), associated with the magnetite and ilmenite series, respectively. These classes provide useful information regarding the internal magnetic zoning in the plutons, which can be associated with mineralizations of mainly Au and Cu. Mainly, the magnetite series (group 2) delimited more perspective zones for mineral exploration. This zoning in MS could guide future mineral exploration in both plutons.
La cartografía del potencial mineral se fundamenta en la elaboración de modelos de probabilidad de ocurrencia de depósitos minerales, como base para el pronóstico metalogénico y la delimitación de áreas perspectivas. La región noreste de México ha sido cubierta por diferentes levantamientos geológicos, trabajos de exploración minera y estudios metalogénicos regionales y actualmente se reportan más de 160 depósitos y manifestaciones de fluorita. Sin embargo, no se han empleado los métodos que permiten el tratamiento, análisis e integración de las guías de exploración utilizados en la cartografía predictiva de potencialidad minera . En este contexto, surge la necesidad de iniciar trabajos de cartografía predictiva en México, que ayuden a minimizar los costos de la exploración minera por concepto de optimización de áreas potencialmente favorables para el descubrimiento de depósitos minerales. La información geológica, estructural, geoquímica y geofísica disponible del NE de México permite la aplicación de la cartografía del potencial mineral soportada en los sistemas de información geográfica. La metodología se basa en la estructuración de los datos primarios, la superposición ponderada y la integración y análisis de los datos mediante los modelos de lógica booleana y máxima entropía (MaxEnt). Los resultados obtenidos indican que el mapa de potencial mineral ofrece un buen predictor, debido a que se delimitan las áreas más favorables para la presencia de depósitos de fluorita, siendo la densidad estructural el parámetro que más influye con un 28.8% de contribución al modelo de potencialidad mineral.
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